Local anesthetics are the safest and most effective drugs in medicine for the prevention and management of pain.
Effectiveness of a local anesthetic is assessed by its “onset time” and duration. Onset time, also referred to as “latency time,” is the period of time between administration and its blocking effect on sensory and motor nerve sensation (numbing effect.)
For more than 100 years, buffering/alkalinization of local anesthetics has been reported in the scientific literature for improving onset time and making the injection of a local anesthetics more comfortable and less painful. The term “anesthetics buffering”, “alkalinization” and “pH buffering” are medical terms used for optimizing the pH of local anesthetics before injection.
Solutions containing bicarbonate ions are routinely used to buffer the pH of local anesthetics, which are typically acidic, and other parenteral solutions. A commonly used medical bicarbonate solutions is sodium bicarbonate (NaHCO3) mixed with water.
Mixing syringes capable of mixing two fluids within a syringe barrel and delivery of same from a single port for administration/injection have been described. However, the vast majority of these known mixing syringes provide separate chambers for each fluid whereby the chambers are axially aligned, i.e., are “stacked” one on top of the other within the syringe barrel. U.S. Pat. No. 8,353,866 describes a dual-chambered syringe wherein the chambers are configured parallel to one another, or “side-by-side,” within the syringe barrel, for mixing two fluids prior to administration, but this device provides a divided, open lumen for containing the fluids and is not configured to receive a prefabricated carpule of drug and diluent.
Despite the long history of anesthetic buffering, technological advances have failed to make buffering of local anesthetics practical, efficient, or easy-to-use in a clinical setting. Commercially available devices for dispensing buffered local anesthetics involve a high degree of technique and require health care professionals to manually mix the bicarbonate with the anesthetic, on-site, prior to filling of the syringe for administration of the buffered anesthetic.
Prior local anesthetic syringe devices did not control the pH in which the local anesthetic solution exits the syringe device.
Among these deficiencies, conventional methods and devices still have the following disadvantages:                1. The on-site preparation time is greater than the actual time require to administer the same.        2. The buffered anesthetic solution is prepared in bulk, in amounts greater than initially administered, in order to provide for subsequent administrations, if needed; the pH of buffered anesthetic solution can decrease, and activity can diminish, over relatively short time periods.        3. Freshly mixing buffered anesthetic solutions for subsequent administrations require preparation steps (e.g., mixing) to be repeated.        
It is therefore an object of this invention to provide a novel dispensing device and method which can overcome these known disadvantages and deficiencies.